Adhere to default formatting of cells, that is text is aligned to the left and numbers to the right- this is what Excel expects. This can greatly speed up troubleshooting if you having issued with a formulas or referencing cells, as at a glance you can tell if the cells should be formatted and text or numeric.

Keep to universal colours if you can, I find that black, white and grey colours work best, they look neat and professional but give the spreadsheet added value.

Back during the infancy of this software, most people would use it for just two reasons to store data (especially customer database) and as a glorified calculator. Perhaps because those are a spreadsheets intended or more practical uses or that people are not really that trained to use its features to the fullest. You would even be surprised that up to now there are office employees who, when they are prompted to make some calculations, they would open their spreadsheet software and do the calculations there.